The uncertainty of measurement of coordinate-measuring instruments is at present determined predominantly by means of so-called step-end gauges, which are set up in different positions within the measurement range of the coordinate-measuring instrument. With reference to this, there is VDI/VDE Guideline 2617, in which the required structures and method steps are indicated.
It has also been proposed that so-called ball-rod measurements be carried out in order to determine the uncertainty of measurement of coordinate-measuring instruments. According to this method, which is described in "Precision Engineering", Volume 4, No. 2, April 1982, Pages 61-69 and recommended in Standard B 89 of the Bureau of Standards of the USA, a ball rod consists of two steel balls which are connected to each other by a bar of adjustable length. The ball rod is held fast at one end in a magnetic mount on the table of the coordinate-measuring instrument, while the other end of the ball rod is oriented for measurement in different positions; in an alternative method, said other end is moved dynamically via a similar coupling to the probe head of the coordinate-measuring instrument throughout the measurement range of the instrument. These magnetically mounted techniques are for various reasons unsuitable for determining the uncertainty of measurement of high-precision measuring machines; for example, the steel balls become magnetized and dirty in the course of time. Accordingly, the seat of the ball in the magnetic mount cannot be reproduced with sufficient reliability. The ball that is magnetically mounted cannot be contacted by the measuring instrument, and therefore the length of the ball rod, which after all represents the actual reference in determining the uncertainty of measurement, is not measured directly. Furthermore, the setting of the ball rod in different positions on the measurement table of the coordinate-measuring instrument requires a relatively long time.
The dynamic method cannot in any case be applied universally to all coordinate-measuring instruments since a special probe head is required.
Federal Republic of Germany OS No. 36 05 947 discloses a testing device consisting of a support and of a test standard which can be mounted in different orientations on the support. The support has a pivot bearing via which it, and thus the test standard, can be turned rapidly into different angular positions within the measurement range of the coordinate-measuring instrument. Here, however, use is made of a test body which is not in accord with Standard B 89 of the Bureau of Standards. Furthermore, the change of the test body to different orientations on the support is very cumbersome.